Seamless hollow metallic section and process of making the same



c. w. HALL 1,839,919

SEAMLESS HOLLOW METALLIC SECTION AND PROCESS OF MAKING THE SAME Fam 5, E932.

Filed March 26. 1927 INVENTOR ATTORNEY Y Patented Jan. 5,v 1932 PATENT OFFICE CHARLES 'WARD HALL, OF LARCHMONT, N YORK SEAMLESS, HOLLOW METALLIC SECTION. AND PROCESS OF MAKING THE SAME amiii'catnmI med Maren 216, 1927. serial No. 178,632.

This invention relates to closed hollowsections, of duralumin or other alloy of aluminum, steel or a steel alloy, or other suitable metal, and the' object thereof is the producs tion of seamless hollow sections of any desired shape for use, as in the construction of aircraft for example, where a maximum of strength combined with a minimum of weight is the desideratum.

The invention comprises, 'as a new article of manufacture, a section having a differential wall thickness so disposed as to provide at different points in the periphery thereof an effective strength' approximately proportioned to the stresses to which the section will be subjected when in use as designed, and, -as a practical method for the fabrication thereof, the process which brieiiy stated includes the following steps, viz.: A hollow billet, preferably a length of cylindrical tubing, is formed, by extrusion or by extrusion and drawing for instance, ofthe requisite size and of a wall thickness equal to `or slightly ,greater than the maximum Wall thickness of the desired section. A suitable mandrel is inserted within the billet, which in the case of tubing is usually first flattened somewhat on opposite sides for the purpose,

and thereupon the billet with Ythe mandrel therein is passed through a rolling mill the rolls" of which are brought closer together in the usual way after eaclf'pass, thus progressively'thining those portions of the billet wall between the rolls and the adjacent surfaces of the mandrel and at the same time correspondingly increasing the peripheral measurement of the tube wall,`with intermediate heat treatments as required, untilthe requisite wall thickness :has been obtained. The resulting section is then reformed to the finished section desired by one or two passes through appropriate dies. In such final passes there must be a reduction in the crosssectional area of the wall sufficient to cause a set of the metal, so that` it will retain the` shape of thedies, and sufiicient also, if annealed just prior to the final drawing, to refine the grain. `f 5t I For a full understanding of the invention reference is made to the accompanying drawings, Whereln- Figure l 1s an end vlew of a tubular billet,

,in the form' of tubing; Fig. 2 is an end view showing the billet slightly flattened top and 55 bottom and Vwith a mandrel inserted therein ready for rolling; Figs. 3 and 4 are end views of slightly modified forms of the mandrel; Fig. 5 is an end view of the 'rolled section after ait has been reformed to circular shape; 6o and Figs. 6, 7 and 8 are end views, on an enlarged scale, of finished sections of three different types.

As here shown A is the tubular billet, and A1 (Fig. 2) indicates the same after it has 65 been flattened top and bottom and the mandrel B has been inserted therein. The tubing, with the mandrel in place therein, is now ready for rolling. Specially formed rolls may be used for the purpose, but'it is entirely 70 practicable to obtain any desired rate of change of thickness in the tube wall with the usual straight rolls and these are accordingly preferred as being more economical. The rolls are preferably set,\and brought together after each pass of the tube, so as toreduce the tube wall thickness on a single pass from about 5 to approximately 25 per cent.

The mandrel B is shown in Fig. 2 as having flat upper, and lower surfaces x m which are slightly eased or rounded at the corners vf y, which easing is no more than the reduction of the tube wall thickness which takes place on' a single pass bet-Ween the rolls. In

thinning the tube walls in this way the ma 85,

terial is caused to flow, so as to increase the original periphery of the tube. Hence, with a mandrel shaped as shown in Fig. 2, a decreaseJ in the tube wall thickness of say 10 per cent. on each pass bet-Ween the rolls will produce an' increase of about the same *per cent. of the width of the mandrel in the peripheral. measurement of the tube, so that, when portions of the tube wall have been reduced to a minimum of about 50 per cent. of

their original thickness the tube will be substantially of the size and shapeshown in dotted lines in Fig. 2. Variations in the thickness and width of the mandrel relative 190 gerated scale at a c and d, Fig. 5. rl`he result-ing ridges, while practically inperceptible, will be removed and so provide a smooth inner surface if, in passing the section tln'ough the reshaping or finishing dies, a suitably shaped core is used.

lVhen the upper and lower surfaces of the mandrel used have a slight convex curvature, as shown, somewhaty exaggerated, at m af in the mandrel B1 (Fig. 3), the taper produced in the wall thickness of the section will be ext-ended from the sides inward to the center of the mandrel; and if one ofthese surfaces has a curvature somewhat greater than that of the other, as at m in the mandrel .B2 (Fig. 4), the taper in the wall thickness will be steeper on one side than on the other side of the tube, as illustrated in the finished section shown in Fig. 8.

Figs. 6, 7 and 8 illustrate three finished sec# tions suitable, respectively, for spars of d lunbbell and of approximately elliptical section and struts of stream-line section. In the inal reforming of the section`it should, as already stated, be drawn sufficiently to enable it to retain fully the shape of the dies and. annealed just prior thereto, to refine the grain in the metal.

No practical method of forming my new sections by drawing only has as yet been found, and if some way of so doing should later be discovered it is believed that the cost thereof would be prohibitive.

vVhat I claim as new, and desire to secure by Letters Patent, is

l. The method of fabricating seamless closed hollow sections with differential wall thickness which com rises as a step therein forming a hollow bil et of suitable diameter and with walls of a thickness at least equal to the maximum wall thickness of the desired section and then progressively thinning and laterally expanding portions of its walls on the opposite sides of the same axis thereof.

2. |lhe method of fabricating seamless closed hollow sections with differential wall thickness which comprises as a step therein progressively rolling down portions only of the walls of a hollow billet against the opposite approximately plane surfaces of a mandrel inserted therein.'

3. The method of fabricating seamless closed hollow sections with dierential wall thickness which comprises forming a hollow billet, inserting'therein a mandrel having upper and lower surfaces convexly curved so slightly if at all as to be approximately parallel, and progressively rolling down the walls of the billet against said mandrel surfaces by successive passes of the tube and mandrel between a pair of rolls.

4. The method of fabricating seamless closed hollow sections with differentialwall thickness which comprises forming a tubular billet, slightly flattening the billet and inserting therein a` mandrel having approximately plane upper and lower surfaces, and

progressively rolling down. portions of the tube walls against said surfaces of the mandrel by successive passes of tube and mandrel between a pair of rolls, the rolls being brought slightly closer together at each pass of the tube therethrough.

5. The method of fabricating seamless closed hollow sections with differential wall thickness which comprises forming a hollow billet of suitable diameter and with walls of a thickness at least equal to the maximum thickness of the desired section and then progressively thinning and laterally expanding portions only of the walls ofthe billet on the vsame opposite sides thereof and occasionally during such thinning process subjecting the walls of the billet'to heat treatment.

6. The method of fabricating seamless closed hollow sections with differential wall thickness which comprises `forming a tubular billet, progressively thinning portions of its walls on opposite sides thereof between the approximately plane upper and lower surfaces of a mandrel inserted within the billet and a pair of rolls, and finally reforming the section in manner to provide Ya finished sectionhaving a wall symmetrically tapered in thickness on the opposite sides of one of its principal axes.

7. The method of fabricating seamless closed hollow sections with differential wall thickness which comprises forming a tubular billet, flattening the billet for the purpose and inserting therein a mandrel having approximately plane upper and lower surfaces, progressively thinning the tube walls against said surfaces of the mandrelv by repeated passes of the tube and mandrel between a pair of rolls, and reshaping and drawing down the rolled section sufficiently to cause a set of the metal by passing the same through a suitable die.

CHARLES WARD HALL. 

